The advantages of micropropogation are well known. It offers a convenient and effective method of disease control with consequent improvement in plant quality. Freedom from disease is becoming an increasingly important attribute in relation to quarantine retirements imposed in promising export markets such as the Middle East.
Micropropogation provides a method of rapid plant multiplication. In addition to its general significance as a means of achieving dramatic increases in quantity it confers specific benefits. Production of commercial quantities of a new variety can be achieved by a manual micropropogation in approximately 50% of the time required by conventional methods. The facility to rapidly build up numbers of new varieties is important even for species, such as vines, that are easily propagated by cutting.
The micropropogation technique enables the more productive use of space. Subculturing is conducive to the achievement of a pleasingly high rate of utilisation of laboratory space. Better utilisation of glasshouses and plant "hardening" space is also encouraged. Where seasonal markets are being served, rapid multiplication of varieties avoids the necessity to leave unoccupied space in stock houses for protracted periods while numbers are being built up. Operation can be continued at any time of year under controlled conditions of temperature, light cycle and nutrient balance. Culture storage or reduced temperature can be used to reduce growth rate to produce synchronised high output for seasonal demand.
Application of micropropogation to a species requires the identification of a satisfactory relationship between the plant material, culture medium and incubation conditions. The range of species for which a standard procedure for micropropogation has been devised is rapidly increasing with a consequent growth in the potential area in commercial application.
The sequence of operations involved in micropropogation by organ culture is briefly as follows:
(i) Initial culture; shoots are taken from the selected plant, surface sterilised and placed onto a sterile medium. PA0 (ii) The buds on these shoots eventually develop and these are subcultured to shoot multiplication medium (SM). PA0 (iii) The shoots grow rapidly on SM producing a large number of clonal shoots. To increase the number of shoots and to maintain the line, the shoots are subcultured to fresh SM every 3 to 4 weeks. PA0 (iv) Roots develop when a sample of the shoots are sub cultured to a rooting medium (RM) in a petri dish or similar container.
The plants are usually dispatched in stacks of containers. The recipient removes them from the containers under non-sterile conditions and "hardens" them to outside conditions in a high humidity environment.
Subculturing is usually performed in a transfer chamber where the shoots are removed from their containers with sterile forceps, dissected, usually quite roughly, with a sterile scalpel into small clumps of shoots or single shoots and then placed onto fresh medium. Pieces cut so as to not contain sufficient whole meristem cells will grow slowly or not at all. Plants containing few or no whole fully differentiated cells are liable to not generate as "true to type" or clonal plants.
The largest cost in the procedure is the labour involved in subculturing the shoots from one medium to another. The cost of subculturing is at least three times the cost of all the other procedures.
The reason for this can be illustrated in terms of the subculturing of trees. Here the performance of 5000 transfer operations per day is an absolute maximum for a technician. Similar productivity constraints apply to these operations whether conducted at macroscopic or microscopic scales. In addition in many laboratories sterility control is incomplete, so that contamination losses can be very substantial. Cleaning, preparation, control and movement of plant containers between cutting, storage and hardening areas and transfers to hardening medium are also very labour intensive.
Due to the intricacy of the handling and cutting operations required and the fragile nature of the plant material, it has been extremely difficult to develop apparatus to assist in these processes which will perform as required without damaging the delicate plant tissues.
Thus, the present ability of the Australian and Overseas nursery industry to satisfy the demand for micro propagated plants is severely constrained by the cost of the manual cutting process and transfer processes presently employed in the micropropogation process and the maximum number of operations per day which may be performed by even the most skilled operator without deleterious side affects.
It is therefore an object of this invention to provide an apparatus for dividing plant materials that will overcome, or at least ameliorate the above disadvantages.